Comparisons of various density functional theory (DFT) methods at different basis sets in predicting the molecular Structures and C-13 NMR spectra for [Pt(en)(CBDCA-O, O')], an analogue of the antitumor drug carboplatin, are reported. DFT methods including B3LYP, B3PW91, mPW1PW91, PBE1PBE, BPV86. PBEPBE, and LSDA are examined. Different basis sets including LANL2DZ, SDD, LANL2MB, CEP-4G, CEP-31G, and CEP-121G are also considered. It is remarkable that the LSDA/SDD level is clearly superior to all of the remaining density functional methods ill predicting the Structure of [Pt(en)(CBDCA-O, O')]. The results also indicate that the B3LYP/SDD level is the best to predict C-13 NMR spectra for [Pt(en)-(CBDCA-O, O')] among all DFT methods.